1. Field of the Invention
The present invention pertains to the field of computer systems. More particularly, this invention relates to the dynamic management of processor performance and power consumption in a portable computer system.
2. Background
Recent portable computer systems such as laptop computers and palmtop computers typically contain a central processing unit and a variety of input/output devices such as a keyboard, a display device, and mass storage devices. Typically, such a portable computer system includes a battery subsystem that provides power to the computer system while alternating current power is not available. Such a battery subsystem is typically capable of supplying a limited amount of electrical current to the computer system before requiring a recharge or replacement.
Such a prior portable computer system typically provides a variety of mechanisms for minimizing the electrical current consumption in the computer system. For example, such systems usually implement sleep modes and standby modes for the input/output devices that reduce electrical current consumption while the input/output devices are not in use. In addition such prior systems typically provide a clock speed control mechanism for the central processing unit.
Typically, the central processing unit in such a system consumes less electrical current at lower processor clock speeds. Unfortunately, such lower power consumption is typically achieved at the expense of performance by the central processing unit. The instruction throughput of such a central processing unit usually decreases in proportion to the decrease in the processor clock speed. As a consequence, the user of such a prior portable computer system must typically choose between a high performance, high power consumption state for the computer system or a low performance, low power consumption state for the computer system.
The consequences of slower processor clock speeds in such a computer system depends upon the function being performed by the executing program. The user typically does not perceive a significant reduction in performance during interactive functions while the processor is running at a slow clock speed. However, the user does perceive a significant degradation in performance during processor intensive functions at a slow clock speed. Such processor intensive functions are also referred to as processor bound functions.
For example, the user typically does not perceive a significant degradation in performance if the processor is set in a slow clock speed during interactive data entry and typing functions in a word processing application program However, the user does perceive a significant degradation in performance during processor bound functions such as the reformatting of pages, the rendering data to a printer, the drawing complex diagrams or the reindexing data bases.
In such a prior system, the user may select a maximum performance level by setting the processor clock speed to a high frequency. In such a maximum performance mode, the user perceives maximum performance during processor bound functions. Unfortunately, the user typically experiences a significantly reduced battery life in such a high performance mode.
On the other hand, the user may select a maximum conservation mode by setting the processor clock speed to a low frequency. In such a conservation mode, the user typically experiences extended battery life without a perceivable degradation in performance during interactive functions. Unfortunately, the user perceives significant degradation in performance during processor bound functions in such a maximum conservation mode.
In some prior portable computer systems, the user typically selects a desired processor clock speed using a function key sequence or a control panel graphical select function. Some prior portable computer systems allow the user to set the processor clock speed at any time without restarting the computer system. Nevertheless, such typical prior processor clock speed control mechanisms are too cumbersome to provide the user with any useful control over the balance between processor performance and system power consumption.